Our main objective is the demonstration that prostaglandins influence the growth of any of several transplanted tumors in mice, in rats, in rabbits, in hamsters, and in chickens or the growth of spontaneous tumors in mice. All of the host animals will be immunized with several of the prostaglandins and their metabolites and rates of growth of the tumors will be correlated with the binding constants of the anti-prostaglandins produced by this active immunization. Parameters of tumor growth will include wieght of the tumor excised at various times after transplantation, death of the host animal, and prostaglandin cyclic 3', 5' AMP and cyclic 3', 5' GMP content of the tumor.